Accelerometer unit



Oct. 9, 1951 C, M. HATHAWAY 2,570,672

ACCELEROMETER UNIT Filed Jan. 10. 1950 36 y www I@ Patented Oct. 9, 1951UNITED STATES PATENT OFFICE ACCELEROMETER UNIT Claude M. Hathaway,Littleton, Colo.

Application January 10, 1950, Serial No. 137,840

The-present invention relates to accelerometers and more particularly toa compact relatively vaccurate accelerometer unit particularly suitedfor electrical recording of high velocities.

In the operation of aircraft and jet propelled craft and missiles, it isdesired to provide a record of the acceleration in order to analyze theoperating characteristics and performance of each device. In making suchrecords, the accelerometer must be capable of withstanding severestrains due to high accelerations and velocities and yet must providereliable and accurate indication.

Claims. (Cl. F11-119) For recording acceleration, it is highlydesirimproved accelerometer is provided having `a` .plurality ofmagnetic coils so arranged that acceleration operating upon a seismicmass or weight will increase or decrease the impedance lof coils toproduce an electrical change which can be translated into an indication.In addi tion to a rugged and accurate structure, means must also beprovided to produce the necessary damping action to avoid spuriousindications.

It is, therefore, the object of the present invention to provide animproved accelerometer unit for electrically producing an indication orrecord of acceleration and deceleration of bodies moving at relativelyhigh velocities.

It is a further obiect of the present invention to provide anaccelerometer unit which has a Vhigh degree of accuracy and yet iseconomical to manufacture.

A still further object of the present invention lis to provide animproved accelerometer unit having a convenient and simple arrangementfor adjusting the unit during its manufacture.

Other and further objects of the present invention subsequently willbecome apparent by reference to the following description taken inconjunction with the accompanying drawing wherein:

Fig. 1 is a cross sectional view of an accelerometer unit constructed inaccordance with the teaching of the present invention; Y i

Figure 2 is an end view of the unit shown in Figure 1 with one elementthereof partially broken away;

Figure 3 is an electrical circuit diagram illustrating the manner inwhich the unit in Figure lis employed to produce an indication; and

Figure 4 is a view as seen in the direction .of the arrows along theline 4 4 of Figure 1.

Referring to Figures 1 and 2,.it is to be noted that the accelerometerunit has a casing I I which has a spool-like cross sectionalVconiiguration. The casing II embodies a relatively large chamber I2 andI3 at the ends of the casing which chambers are interconnected by acylindrical elongated passage I4. Adjacent one end an expansion chamber20 is provided which has one Wall I5 formed of a synthetic elasticmaterial. The expansion chamber 20 is connected -to the other chambersby relatively small aperture I6.

The chamber I2 is divided into two compartments by a diaphragm I1 whichhas a central threaded aperture formed by a nut I8. The diaphragm I1 hasa relatively small aperture I9 which serves as a passage communicatingbetween the two compartments of chamber I2 to permit damping fluid toflow from one compartment to the other.

The chamber I3 is divided into two compartments by a similar diaphragm2| having a threaded nut 22 at a center and also being provided with arelatively small aperture 23 to permit damping ud to flow from onecompartment to the other. Extending between the diaphragms I1 and 2| isa tubular` or cylindrical member 24 which is preferably formed of anonmagnetic material and may be one of the plastic materials. Each endof the member 24 is provided with a threaded portion such as thethreaded members 25 and 26 which iit into the threaded apertures or nutsI 8 and 22. The middle portion of the cylindrical member 24 is providedVwith a magnetic sleeve 21 which is centered relative to the coilssurrounding the central passage I4. When the member 21 is properlycentered by adiustment, the adjustment may be retained by theapplication of a small quantity of solder to the threaded ends 25 and 26of the member 24.

It will be noted that extending radially from the walls of thecylindrical passage I4 are partitions 28 and 29 so as to providesuitable boundaries for a plurality of coils 3|, 32, and 33.

As may be seen from Figure 3, the central coil 3| is arranged to beenergized from a suitable source of alternating current 34 which is ofcarrier frequency of several thousand cycles per second. The coils 32and 33 are connected in series and across a plurality of voltagedividers 35 and 3B. The common juncture between the coils 32 and 33 inthe one case is connected through a capacitor 31 to the movable contactof the voltage divider 35. In the other case, the movable contact andthe voltage divider 36 is connected directly to the juncture of the twocoils 32 and 33. A by-pass capacitor 38 is connected across the voltagedividers 35 and 36. The voltage dividers 35 and 36 are connected to theinput of an amplifier and discriminator 39 which corresponds generallyto the circuit arrangement disclosed in Hathaway Patent No. 2,431,420 orto theionejdisclose'd 4 in Hathaway Patent "No 2,445,880. To the outputof the amplifier and discriminator is connected a visual indicator 'oermeter 4I which preferably is of the zero center type so that anindication may be livd fof -'th""e magnitude and direction ofmovementkglwthe magnetic core 21 depending upbnfaccdele'r'ation ordeceleration being present. c Y. Y.

The adjustable contacts provided for the voltage dividers 35 and 36 arearranged t'c'vide phase compensation so that accurate voltages lied tothearnplrfand "discriinator t t "lltins g"`slaid`lc`hamb rs,ap'luralityof diaphfa ms vide A'each'Y cliafnberi 3. An accelerometercomprising a housing having two large chambers spaced apart andinterconnected by an elongated passage, a plurality of electromagneticwindings surrounding said passage, a plurality of diaphragms each havinga central threaded aperture and being mountedV to divide eachchamberinto compartments, each Y diaphragm having` a relatively smallaperture therein to interconnect :said compartments, a

l5 small aperture.

An aclerbmeter' comprising ahousing havingutwojlargeqhambers at each endintercon-V 'nectedhby an elongated cylindrical passage, a plralitylofelectromagnetic windings mounted 2o on the exterior of saidhousing andsurrounding qsaid'flpassage, -a plurality of diaphragms each havinglacentral threaded-aperture'fand bei-xg 'Y "mounted Pt'o 'divide e'ach4chamber 'into compart-V ments, each diaphragmhavinga-relativ'el-yl-small 25 damping 'aperturetherein, anda'mova-blem'agnetic tube 7having fthreaded "ends f'in lengagement with thethreaded apertures of 'saiddiaphrgns Yand carrying kat the middle va'magnetici-sleeve Y 5. -An `accelerometer comprising'a )housinghav- 30ing two large uchambers-attach endintercon- Ynected -by -an elongatedcylindrical passagefa plurality f fof -electromagnetic 'windings mountedon the exterior of said housing and surrounding saidfpassage, apluralityof V7diaphragms'each'lavr35 ing a central threaded aperture and beingmounted-to Vdivide each 'chamber v`into' compartments, each diaphragm-having-a relatively e.small damping aperture therein, -andf a movablevimag'- Anei-.ic tube having 1.tlrrea'cled' ends in--engagement Ywithvthe threaded apertures yof`said` diaphragnis andV 'carrying at v-themiddle ^a emagneticsleeve,

Nand an expansion4 chamberfformed in 4v(inerenti ofsaid-housing-'interconnected vby rawrelativelfy small passage -to Y'saidrst chambers, 'and a d iapl'lragrrr*for-said expansion chamber fform'edof syntheticelastic-material 4hav-ing "one surface exposed-to-theatmosphe1 e.. CLAUDE M. -HA-THAWAY.

RlElfElt-"ErCEs `'CITED -'folll'l'win'g references are ofrecordinte fileof this patent: UNTED `sTATE`s1=frETs

